Effect of femoroacetabular impingement (FAI) on hip motion in young adults Femoroacetabular impingement (FAI) is an increasingly recognized source of hip pain in young adults and has been implicated as a cause of labral injury and hip osteoarthritis (OA). FAI is a structural abnormality of the acetabulum (pincer FAI) or femur (cam FAI) which results in impingement between the acetabulum and femur during hip flexion and internal rotation. Current treatment for FAI includes surgical procedures to resect or reorient the femur or acetabulum or both. The number of FAI surgeries being performed in the US is estimated at 50,000 per year, with an annual growth rate of 15%, indicating that FAI is a growing health concern. While structure does contribute to hip pain, increasing evidence suggests that movement patterns also play an important role. The overall goal of this line of research is to improve treatment for hip pain, especially in young adults, prevent or slow the progression of chondral damage, and reduce the need for hip arthroplasty. The purpose of this project is to assess the movement patterns of people with painful FAI compared to people without hip pain and to test for pathology-specific and limb-specific differences in these patterns Identification of differences in movement patterns which may contribute to hip pain can improve non- invasive treatment for people with hip pain. To test for these differences, we will assess movement patterns using kinematic data collected during tasks including walking, running, stepping down and up, single leg squat, supine straight leg raise and prone hip extension in subjects with painful FAI and subjects without hip pain. We hypothesize that subjects with painful FAI will display movement patterns which are closer to the end of their available range of hip flexion, adduction and internal rotation than subjects without hip pain. We believe that these movement patterns contribute to a subject's hip pain. Based on the distinct patterns of joint damage between the two types of FAI, we hypothesize that people with pincer FAI will display different movement patterns than people with cam FAI. The knowledge gained from this research has the potential to redirect treatment for people with FAI by identifying movement patterns that could be targeted by inexpensive and non- invasive therapeutic interventions such as neuromuscular retraining.